Preliminary investigations indicated that each of the dissociation products of H2CO3 destroy tooth enamel producing decay similar to, if not the same as, initial caries. The enamel demineralization was rapid at pH 5 indicating predominantly H plus actions. Enamel mineral dissolution was slow at pH 7 indicating little H plus action. However, the enamel softened and changed to opaque white appearance in HCO3 minus solution indicating a significant change in physical and chemical properties of the mineral. These results, and results of others, suggest that the CO2-H2CO3-HCO3 minus - CO3 minus 2 system in dental plaque and the mineral-water in enamel are a continuum in which distribution and concentrations depend on pH, Pco2, and the diffusibility of the non-ionic CO2 and H2CO3 molecules. The objective of this work is to confirm that dental plaque organisms produce CO2 in amounts to support its diffusion into enamel water where H2CO3 is formed and dissociated to yield locally high concentrations of H plus and HCO3 minus; and that these products dissolve enamel minerals, and leave residual minerals more soluble than enamel. The low levels of fluoride ions known to prevent caries will be studied to determine F minus and carbonic acid system interactions during enamel demineralization and remineralization. The F minus ion effect of increasing the rates of enamel remineralization and of inhibiting dental caries may act by competition with HCO3 minus ions in the enamel. The physical changes and chemical composition (Ca, PO4, CO2 and F) of surface minerals of enamel will be determined after reactions in carbonate solutions with and without F minus ions in solutions over the pH range that occurs in dental plaque.